What is a Tropical Cyclone?

Tropical Cyclones are low pressure systems. In the Southern Hemisphere, tropical cyclones well-defined clockwise wind circulations with a region surrounding the centre with gale force winds (sustained winds of 63 km/h or greater with gusts in excess of 90 km/h). The gale force winds can extend hundreds of kilometres from the cyclone centre. If the sustained winds around the centre reach 119 km/h (gusts in excess of 170 km/h), then the system is called a severe tropical cyclone. These are referred to as hurricanes or typhoons in other countries.

The circular eye or centre of a tropical cyclone is an area characterised by light winds and often by clear skies. Eye diameters are typically 40km but can range from under 10km to over 100km. They eye is surrounded by a dense ring of cloud about 16km high known as the eye wall which marks the belt of strongest winds and heaviest rainfall.

Tropical cyclones derive their energy from the warm tropical oceans and do not form unless the sea-surface temperature is above 26.5°C, although, once formed, they can persist over lower sea-surface temperatures. Tropical cyclones can persist for many days and may follow quite erratic paths. They usually dissipate over land or colder oceans.
Most of the northern coastline of Australia is covered by the Bureau of Meteorology’s weather watch radar network.

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Monitoring Cyclones

Research has shown that cyclones in the Australian region exhibit more erratic paths than cyclones in other parts of the world. A tropical cyclone can last for a few days or up to two or three weeks. Movement in any direction is possible including sharp turns and even loops.

To monitor the progress of cyclones visit the Bureau of Meteorology tracking and threat maps here.

These maps show the past track of the cyclone and the predicted track with distinctive colouring to depict watch and warning zones. A Cyclone Tracking Map can be downloaded here.

Tropical Cyclone Outlook
Outlook statements are issued daily by each Tropical Cyclone Warning Centre. These present 3-day outlooks on possible tropical cyclone development in the region and surrounding oceans.

Tropical Cyclone Information Bulletins
Bulletins are issued every six hours if a tropical cyclone exists within the Australian region, but is not expected to threaten any coastal or island communities within the next 48 hours. Bulletins include the cyclone’s name, current location and its forecast movement.

Tropical Cyclone Watch
A watch is issued every six hours when there are indications that gales or stronger winds are expected to affect coastal or island communities within 48 hours but not within 24 hours. It details the communities expected to be affected and gives a brief estimate of the cyclone’s location, intensity, severity category and movement.

Tropical Cyclone Warning
A warning is issued every three hours when there are indications that gales or stronger winds are expected to affect coastal or island communities within 24 hours. As well as information provided in a watch advice, warning advices also inform of expected maximum wind gusts. Forecasts of heavy rainfall, flooding and abnormally high tide are including where necessary. Communities under threat are also advised to take precautions necessary to safeguard their lives and property. When a cyclone is under radar surveillance close to the coast, hourly advices may be issued.

The general name given to Tropical Cyclone Watch or Warning messages is an Advice or Tropical Cyclone Advice. A tropical cyclone advice is prefixed “FLASH” when it is the first warning to a community not previously alerted by a cyclone watch. It is also issued when major changes are made to the previous warning due, for example, to unexpected movement towards the coast or rapid intensification.

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Cyclone Severity Categories

Categories of cyclone severity range from 1 for weak cyclones to 5 for the most severe cyclones.

Category
1

Typical effects (indicative only)
Average wind (km/h)
63-90
Strongest Gust (km/h)
Less than 125
Central Pressure (hPa)
Greater than 985
Negligible house damage. Damage to some crops, trees, caravans. Craft may drag moorings.
Category
2

Typical effects (indicative only)
Average wind (km/h)
90-120
Strongest Gust (km/h)
125-170
Central Pressure (hPa)
985-970
Minor house damage. Significant damage to signs, trees, caravans. Heavy damage to crops. Risk of power failure. Small craft may break moorings.
Category
3

Typical effects (indicative only)
Average wind (km/h)
120-160
Strongest Gust (km/h)
170-225
Central Pressure (hPa)
970-945
Some roof and structural damage. Some caravans destroyed. Power failures likely.
Category
4

Typical effects (indicative only)
Average wind (km/h)
160-200
Strongest Gust (km/h)
225-280
Central Pressure (hPa)
945-920
Significant roofing loss and structural damage. Many caravans destroyed and blown away. Dangerous airborne debris. Widespread power failures.
Category
5

Typical effects (indicative only)
Average wind (km/h)
More than 200
Strongest Gust (km/h)
More than 280
Central Pressure (hPa)
Below 920
Extremely dangerous with widespread destruction.

An estimate of cyclone severity is now included in all tropical cyclone advices. The tables above provide information concerning effects due to wind, which are typical of cyclones in the various categories. Remember that the system is not designed to give an exact statement of conditions at individual locations but will give a general idea of the expected worst conditions.

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How to Prepare for the Cyclone Season

For general information on preparing for cyclones please download the Department of Emergency Services Preparing for Cyclones Booklet here. This information is also available in other languages here.

Preparation

Even if previous cyclones have not moved over your area this is no guarantee that future cyclones will miss you. The following actions will help to ensure you, your family and your home is prepared in the event of a disaster.

You should aim to complete the following preparations by 1 November every year:

  • Preparing for Cyclones‘ brochure in English, Japanese, Chinese, Korean, Hmong, Italian and Samoan.
  • Your pre-season check should include tree trimming and de-nutting coconut palms. Keep your garden tidy of rubbish and leaf litter and ensure that trees and branches are clear from your home and overhead power lines. Do not attempt to clear trees from power lines yourself – call Ergon Energy on 13 10 46 for advice.
  • Check the walls, roof and eaves of your home are secure. Ensure any works carried out meet the latest building regulations.
  • Preferably fit shutters or metal screens to all glass areas.
  • Clear your property of loose material that could blow about and potentially cause injury or damage during extreme winds.
  • Speak with your family about the effects of cyclones and floods, and prepare a Family RediPlan. Members of your family that may be disabled or elderly will need more time to prepare and to evacuate if necessary: consider their special needs.
  • Check neighbours, especially recent arrivals and the vulnerable to ensure they are adequately prepared.
  • Keep your car regularly fuelled.
  • Ensure your emergency kit is fully stocked.
  • Have a good stock of tinned food for the family and any pets. As a guide, you should plan for 7 days in urban areas, 1 month in rural areas and for 3 months in remote areas)
  • Have alternative cooking equipment, for example a gas BBQ.
  • Consider having a generator connected to your home. This should be undertaken by a suitably qualified electrician.
  • Have a listing of important phone numbers handy.
  • Some phones (e.g. cordless) will not work in a power failure. Ensure you have a back up telephone which plugs straight into the telephone line.
  • Click here for advice if you plan to be away or on holiday during cyclone season.

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What do to when a Cyclone Watch is issued

As a cyclone moves closer towards the coast a Cyclone Watch will be issued. At this stage the following actions should be completed without delay:

  • Regularly tune into local radio / TV to monitor information.
  • Re-check your property and secure loose items, for example pot plants, hardware, outdoor furniture and rubbish bins.
  • Remove valuable items off the floor and away from windows in case of flooding and flying debris.
  • Check emergency kit and ensure household members are aware of its location.
  • Ensure household members know which is the strongest part of the house and what to do in the event of a cyclone warning and / or evacuation.
  • Check that neighbours are aware of the situation and are preparing.
  • Secure valuable items in a waterproof container you are also able to evacuate with if necessary
  • Fill your bath, laundry tub and appropriate containers with water, in the event the water supply is cut. Freeze water for alternative refrigeration should there be a power failure.
  • Fill your vehicles fuel tanks.

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What to do when a Cyclone Warning is issued

  • Stay tuned to local radio / TV for further information.
  • Collect children from school or childcare centre and go home.
  • Park vehicles under solid shelter (handbrake on and in gear). Click for additional guidance for boat owners.
  • Put wooden or plastic outdoor furniture in your pool or inside with other loose items.
  • Close shutters or board / tape all windows and secure all doors. Draw curtains and lock all doors.
  • Pack an evacuation kit of warm clothes, essential medications, baby formula, nappies, valuables, important papers, photos and mementos in waterproof bags to be taken with your emergency kit. Large/heavy valuables could be protected in a strong cupboard.
  • Remain indoors (with your pets). Stay tuned to your local radio/TV for further information.

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